1. Field of the Invention
The present invention relates to electrical wiring devices and particularly to a strain relief for electrical cordsets.
2. Description of the Related Art
A particular problem that has historically plagued electrical cordsets is conductor breakage at a point adjacent the exit of the electrical cord from connectors electrically terminating the cordset. Particularly in the case of light duty cordsets where the conductor size is 18 gauge or smaller, the electrical cord is extremely flexible. During normal use, the cord is typically subjected to flexure-induced stresses concentrated at a point where the cord exits the electric connector terminating the cordset. At this point of connector exit, the cord is no longer constrained and thus is free to bend on an extremely small radius. During normal use over years of service, the cord is repeatedly flexed in opposite directions about opposed fulcrums where the connector engages the cord at the exit opening in the connector body from which the cord emerges. Consequently, the high stress in the copper conductors of the cord are concentrated at this exit point where flexure or bending begins. In time, the copper conductors can be fatigued to the point of breakage. The resulting loss of electrical continuity renders the cordset useless.
In recognition of the problem, manufacturers have resorted to using semi-rigid polyvinyl chloride molding materials for the connector so that a relatively flexible sleeve can be included to surround an extended portion of the cord exiting the connector. This strain relieving sleeve enforces a larger bend radius on the cord as it undergoes flexure. When the bend radius is increased, less stress is concentrated in the cord conductors at the initial flex point where the cord emerges from the sleeve. Thus, work hardening and fatigue of the cord conductors are reduced. However, the use of semi-rigid vinyl connectors with strain relieving sleeves has the disadvantage of added material and manufacturing costs and poor elevated temperature performance. Rigid plastic molded materials are preferable because of lower manufacturing and material costs and superior elevated temperature stability.
Underwriter Laboratories (UL) and the Canadian Standards Association (CSA) have devised a safety/performance test that manufactured cordsets must pass in order to be listed. This test requires that a cordset undergo a 2500 cycle flex test which involves suspending a 4 oz. weight from the cord, while the connector is rotated through a 180.degree. sweep, 2500 times. The cordset passes, if at the end of this extremely rigorous test, the cord conductors retain continuity.